In a wireless communication system, the wireless portable Internet is a next-generation communication system that supports mobility and local area data communication such as in a conventional wireless local access network (LAN) that uses a fixed access point.
In such a wireless portable Internet system, an access terminal (AT) requires a ranging process to access an access point (AP). The ranging process controls transmission power, timing, and frequency offset on uplink so that the AP can receive data from the AT without an error. Thus, the AT periodically transmits a Code Division Multiple Access (CDMA) code to the AP, and the AP estimates values of the transmission power, timing, and frequency offset while receiving the CDMA code, adjusts the estimated values to be within a range for accurate data receipt, and transmits the adjusted values to the AT.
In more detail, the ranging process is broadly divided into an initial stage and an adjusting stage. During the initial stage, the AT selects a resource from among uplink resources provided by the AP and initially accesses the AP by transmitting a CDMA code assigned to the AT to the AP through the selected resource. During the adjusting stage, the AT receives and processes the RNG_RSP message transmitted from the AP that has received the CDMA code to adjust transmission power, timing, and frequency offset on the uplink. The AT periodically performs the initial stage and the adjusting stage at regular intervals.
However, the number of RNG_RSP messages broadcasted by the AP in response to the CDMA code for the ranging process increases as the number of ATs that access the AP increases. As a result, the number of messages processed by the AT increases. In other words, the AT receives and processes all RNG_RSP messages broadcasted from the AP, and thus a load of the AT is increased.